Lightening

CloseThe crust is the thin, solid, outermost layer of the Earth. It is made of rocks and minerals. The crust is not a single piece but is broken into large sections called tectonic plates. The crust is thinnest under the oceans (about 5 km thick) and thickest under mountains (up to 70 km thick).

CloseDischarge is the process by which a charged object loses its excess charge. This can happen slowly (like a charged balloon losing charge over time) or suddenly (like a spark or lightning). Lightning is a massive natural discharge between clouds or between a cloud and the ground.

CloseThe Earth’s lithosphere (crust and upper mantle) is broken into about 15 to 20 large tectonic plates. These plates float on the semi-fluid layer below called the asthenosphere. They move very slowly (a few centimetres per year) due to convection currents in the mantle.

CloseProtons are subatomic particles found in the nucleus of an atom. Each proton carries one unit of positive charge. The number of protons in an atom determines which element it is. Opposite charges attract, so protons are attracted to electrons (negative charge).

CloseElectrons are subatomic particles that orbit the nucleus of an atom. Each electron carries one unit of negative charge. In a neutral atom, the number of electrons equals the number of protons. When an object gains extra electrons, it becomes negatively charged.

CloseThe Richter scale was developed by Charles F. Richter in 1935. It is a logarithmic scale, meaning each whole number increase represents about 32 times more energy released. For example, a magnitude 6 earthquake releases about 32 times more energy than a magnitude 5 earthquake.

CloseA seismograph consists of a heavy weight (mass) that remains still due to inertia while the ground moves during an earthquake. A pen attached to the mass draws a wavy line on a rotating drum of paper. This record is called a seismogram. Scientists analyse seismograms to find the earthquake’s location, depth, and magnitude.

CloseThunder is the sound produced by the rapid heating and expansion of air around a lightning bolt. Lightning heats the air to about 30,000 degree Celsius in a fraction of a second. This hot air expands explosively, creating a shock wave that we hear as thunder.

CloseA tsunami is a series of giant waves caused by the sudden displacement of a large volume of water. This displacement is usually due to an underwater earthquake, but can also be caused by volcanic eruptions or landslides. Tsunamis can travel across oceans at speeds of up to 800 km/h.

CloseA tremor is a minor earthquake or a small shaking of the ground. Tremors can be natural (small earthquakes) or man-made (due to blasting or heavy machinery). Some tremors are so weak that they can only be detected by a seismograph and are not felt by people.

CloseA thunderstorm is a type of storm that produces lightning and thunder. It is caused by the rapid upward movement of warm, moist air, which forms tall cumulonimbus clouds. Thunderstorms also often bring heavy rain, strong winds, and sometimes hail.

CloseLight travels at about 300,000 kilometre per second, while sound travels at only about 343 metre per second in air (at 20 degree Celsius). Therefore, light from the lightning reaches your eyes almost instantly, while the sound of thunder takes several seconds to reach you. The time difference tells you how far away the lightning struck.

CloseThe epicentre is the point on the ground surface that is directly above the focus (the underground point where the earthquake starts). The epicentre usually experiences the strongest shaking and suffers the most damage. News reports always mention the epicentre location of an earthquake.

CloseThe Earth’s crust is the solid, rocky outer layer. It is broken into tectonic plates that fit together like a jigsaw puzzle. These plates are constantly moving, though very slowly. The movement of these plates causes earthquakes, volcanic activity, and mountain formation.

CloseA negatively charged object has an excess of electrons. When it touches a neutral conductor, the extra electrons repel each other and flow from the object to the conductor. This flow of charge continues until both objects have the same potential. This is charging by conduction.

CloseLightning is a massive electrical discharge. When the voltage difference between a cloud and the ground becomes extremely high (millions of volts), the air breaks down and becomes a conductor. A huge current flows, producing intense light (lightning) and heat. This heats the air and causes thunder.

CloseA fault line is a fracture or zone of fractures between two tectonic plates. Most earthquakes occur along fault lines because the plates are moving in different directions — they may collide (convergent boundary), separate (divergent boundary), or slide past each other (transform boundary).

CloseElectrons are negatively charged. When an object loses electrons, it has fewer negative charges than before. The number of positive charges (protons) remains the same. Therefore, the object has an overall positive charge. For example, a glass rod rubbed with silk loses electrons and becomes positively charged.

CloseElectrons carry negative charge. When an object gains extra electrons, it has more negative charges than positive charges. Therefore, the object becomes negatively charged. For example, a plastic rod rubbed with wool gains electrons and becomes negatively charged.

CloseThe Richter scale is logarithmic with base 10 for amplitude, but for energy release, each whole number increase represents about 32 times more energy. So a magnitude 6 earthquake releases about 32 times more energy than a magnitude 5 earthquake, and about 32 × 32 = 1024 times more energy than a magnitude 4 earthquake.

CloseLightning appears as a bright, jagged streak of light in the sky. It can be within a cloud (intra-cloud), between two clouds (cloud-to-cloud), or between a cloud and the ground (cloud-to-ground). Cloud-to-ground lightning is the most dangerous type.

CloseAn underwater earthquake that causes a sudden vertical movement of the seafloor displaces a huge volume of water, creating a tsunami. The waves spread outward in all directions. When these waves reach shallow coastal waters, they pile up into giant, destructive waves.

CloseA microearthquake is a very small earthquake, usually of magnitude less than 2.0 on the Richter scale. These tremors are not felt by people but can be detected by sensitive seismographs. Thousands of microearthquakes occur around the world every day.

CloseWhen lightning passes through air, it superheats the air instantly to about 30,000 degree Celsius. This hot air expands explosively, much faster than the speed of sound. The expansion creates a shock wave that travels outward. When this shock wave reaches your ears, you hear it as thunder.

CloseCumulonimbus clouds are tall, dense, and towering clouds that can reach heights of 12 to 15 kilometres. They are associated with thunderstorms, heavy rain, lightning, thunder, hail, and strong winds. The name comes from cumulus (heap) and nimbus (rain).

CloseThe mantle is the layer beneath the Earth’s crust. It is about 2,900 kilometres thick and is made of hot, dense, semi-solid rock. The mantle moves slowly due to convection currents, which drive the movement of the tectonic plates above it. The crust and the uppermost part of the mantle together form the lithosphere.

CloseSound travels at about 343 metre per second in air. In 3 seconds, sound travels approximately 343 × 3 = 1029 metre, which is about 1 kilometre. To estimate the distance in kilometres, divide the number of seconds between lightning and thunder by 3. So 3 seconds ÷ 3 = 1 km away.

CloseSurface waves travel along the Earth’s surface and are the slowest seismic waves, but they cause the most damage. They produce a rolling or side-to-side motion that shakes buildings and causes the ground to ripple. P-waves (primary waves) are fastest but cause less damage; S-waves (secondary waves) are slower than P-waves but faster than surface waves.

CloseDischarge can happen gradually (leakage) or suddenly (spark). A charged balloon slowly loses its charge because water vapour in the air provides a path for charge to leak away. A spark is a sudden discharge when the voltage becomes high enough to break down the air. Lightning is a giant spark.

CloseThe mantle is very hot near the core and cooler near the crust. Hot, less dense rock rises, and cooler, denser rock sinks. This circular motion creates convection currents. These currents slowly drag the tectonic plates above them, causing them to move a few centimetres per year.

CloseProtons are positively charged and electrons are negatively charged. In a neutral object, the numbers are equal. If an object loses electrons, it now has more protons than electrons, so it has a net positive charge. The object itself does not gain protons; it only loses electrons.

CloseIn deep ocean, a tsunami wave may be only about 1 metre high and travel very fast. But when it reaches shallow coastal waters, the wave slows down and its height increases dramatically. Some tsunamis have reached heights of over 30 metres (about 100 feet), causing catastrophic flooding.

CloseA tremor is the shaking or vibration of the ground caused by seismic waves. Earthquakes can produce multiple tremors. The main shock is the largest tremor. Foreshocks are smaller tremors before the main shock, and aftershocks are smaller tremors after the main shock.

CloseDivide the number of seconds by 3 to get the distance in kilometres. 5 seconds ÷ 3 = 1.67 km. This is a rough estimate because the speed of sound varies with temperature and humidity. At 20 degree Celsius, sound travels at 343 m/s, so in 5 seconds it travels 1715 metres = 1.715 km.

CloseP-waves are the fastest seismic waves. They travel through solids, liquids, and gases by compressing and expanding the material (like sound waves). They arrive first at a seismograph station. S-waves arrive second, and surface waves arrive last. The time difference between P-wave and S-wave arrival is used to find the distance to the epicentre.

CloseAll tectonic plates are constantly moving, so there is no stationary boundary. At convergent boundaries, one plate may sink under another (subduction), creating volcanoes and earthquakes. At divergent boundaries, new crust is formed. At transform boundaries, plates slide horizontally past each other, causing earthquakes.

CloseWhen two different materials are rubbed together, electrons are transferred from one material to the other. Protons are tightly bound in the nucleus and do not move during rubbing. Only electrons, which are loosely held in the outer shells of atoms, can be transferred. The material that loses electrons becomes positively charged; the one that gains electrons becomes negatively charged.

CloseWhen a large earthquake occurs beneath the ocean floor, it can cause the seafloor to uplift or drop suddenly. This displaces a huge volume of water, generating a series of waves — a tsunami. Not all underwater earthquakes cause tsunamis; the earthquake must be strong (usually magnitude 7 or above) and shallow (less than 70 km deep).

CloseA seismograph is sensitive enough to detect even very small tremors (microearthquakes) that are not felt by humans. Networks of seismographs around the world help scientists locate earthquakes quickly. Modern digital seismographs can record a wide range of frequencies and magnitudes.

CloseA building that has a properly installed lightning conductor (lightning rod) is very safe because the conductor provides a direct path for the lightning to reach the ground without harming the building or its occupants. Inside, stay away from windows, doors, and electrical appliances.

CloseThe Earth’s crust is the thin, solid, rocky outer layer on which we live. It contains soil, water, and air. All life on Earth exists on or near the crust. The crust is made of igneous, sedimentary, and metamorphic rocks. The oceanic crust is thinner and denser than the continental crust.

CloseCharge is neither created nor destroyed (conservation of charge). During discharge, the excess charge simply moves from the charged object to another object (like a human hand) or to the Earth. The Earth is so large that it can absorb or supply charge without changing its overall charge.

CloseThe inner core is the Earth’s innermost layer. It is a solid sphere of iron and nickel, with temperatures up to 5,500 degree Celsius. Despite the extreme heat, it remains solid because of the immense pressure from the layers above. The outer core is molten (liquid) iron and nickel.

CloseThe positive rod attracts negative charges in the electroscope to the top (near the rod) and repels positive charges to the leaves. The leaves become positively charged. Since both leaves have like charges (positive), they repel each other and diverge. When the rod is removed, the charges redistribute and the leaves collapse.

CloseP-waves are compressional waves, meaning they push and pull the material in the same direction as the wave travels. They are similar to sound waves. Their speed is about 6 to 7 km per second in the crust. They are the first to be recorded by a seismograph.

CloseThe speed of light is about 300,000 km/s, so you see lightning almost instantly. The speed of sound is about 0.343 km/s (343 m/s). So for every 3 seconds between lightning and thunder, the lightning is about 1 km away. If you hear thunder immediately after lightning, the storm is very close and dangerous.

CloseMinor earthquakes typically have magnitudes between 3.0 and 3.9 on the Richter scale. They are often felt by people but rarely cause damage. Magnitude 2.0 to 2.9 earthquakes are usually not felt. Magnitude 4.0 to 4.9 earthquakes can cause light damage. Major earthquakes are magnitude 7.0 and above.

CloseIn deep water, tsunami waves can travel at speeds of 700 to 800 km/h, which is similar to the cruising speed of a commercial jet aeroplane. However, the wave height in deep ocean is usually less than 1 metre, so ships may not even notice it. The danger comes when the wave enters shallow coastal waters and grows in height.

CloseA fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement. Faults are the result of tectonic forces. Earthquakes occur when the stress on a fault overcomes the friction, causing the rocks to slip suddenly. The San Andreas Fault in California is a famous transform fault.

CloseThunder can sound like a sharp crack (if the lightning is close) or a long rumble (if it is farther away). The rumbling occurs because sound from different parts of a long lightning bolt reaches your ears at slightly different times, and because sound reflects off clouds, mountains, and buildings. The sound of thunder rarely travels more than 25 kilometres.